In the prior art to produce a through-the-board conducting path in a printed circuit board having layers of copper on both sides, the board is first passed through a drilling operation wherein all of the holes to be utilized as conductive holes through the board are drilled. Thereafter, a series of steps are taken in which a heavy layer of copper is ultimately deposited on the walls of each of the holes. This is done by first subjecting it to a catalyst seeding operation wherein microdeposits of metal are placed on the walls of each of the holes. Thereafter, copper is plated out onto the walls of the holes. After all of the holes have thus been plated, the printed circuit pattern is laid out on the two sides of the board and the copper is etched leaving the lead path intact. Thereafter the components are mounted on the circuit board and a soldering step completes the task of securing the component to the board. The holes containing leads to the components are then filled with solder.
In U.S. Pat. No. 3,576,669 the walls of a through hole are coated by passing a rod through the hole and immersing the rod in a liquid metal mixture. The liquid metal adheres to the rod and as the rod is withdrawn from the circuit board the liquid metal is coated onto the walls of the hole. The liquid metal then hardens at room temperature and produces a conducting path between the two sides of the circuit board.